Radio receiver



5ml. 1939. E F ANDREWS 2,143,532

RADIQ RECEIVER Filed April e, 1953 5 sneetssheet l f3 /zf e 1l; A. J\ J [7? were 21074.

E. F. ANDREWS RADIO RECEIVER Filed April 8, 1933 5 Sheets-Sheet 2 Jan. M), V E g:-l ANDREWS RADIO RECEIVER Filed April 8, 1933 5 Sheets-Sheet 5 im. m, w39.. E. FjANDREWs 2,143,532

Y RADIO RECEIVER l Filed April aA 1933 5 sheets-sheet 4 l Harm E. F, ANDREWS 2,143,532

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Filed April 8, 1933 w ..ihhhuhll L l WM if N Patented Jan. l0, 1939 UNITED Vs'rrsrss PATET OFFiCE 11 Claims.

This invention relates to radio receivers and has for one of its objects the provision of an improved radio receiver. y

Among the other objects of the invention are, to provide in a radio set having two units, means for minimizing the loss of signal energy when transferring from one unit to the other, to provide a control unit adapted to modify the signal energy in a highly advantageous manner while maintaining the dimensions of said unit relatively small, to provide an improved automatic volume control, to provide an improved volume level con of the invention;

Fig. 2 is a wiring diagram of a further embodiment of the invention;

Fig. 3 is an illustration of a radio set embodying the invention, the main unit being shown in plan with its cover partly broken away and the remote control unit being shown 'in sectional elevation;

Fig. 4 is an end view of the remote control unit, with its cover partly broken away;

Fig. 5 is an elevation of the main unit, the cover being shown in section in order to display elements normally obscured thereby;

Figs. 6, 7, ii` and 9 are fragmentary wiring diagrams illustrating the means for preventing eX- cessive attenuation of signal energy when transmitted from one unit to the other, and

Fig. 10 is a wiring diagram of a still further embodiment of the invention.

Referring more particularly to Fig. 3, it is to be noted that the main unit, which is designated by the reference numeral 10,15 substantially similar in construction to the set described and claimed in my coepending application, Serial No. 639,821, led October 27, 1932, Patent No. 2,103,135, granted December 21, 1937. This main unit is also shown in Fig. 5 and comprises a base l I which may be of inverted dish shape provided with an outwardly projecting iange I2 to which is secured a closure plate i3. The space between the upper face of the base Il and, the closure (Cl. Z50-20) plate I3 provides accommodation for wiring and small radio parts. A block Hl is mounted in the center of the base l l to serve as a support for the pot l5 of a loud speaker i6. The loud speaker preferably of the dynamic cone type, the cone il being directed upwardly as shown in Fig. 5. A cover i8 ,is supported upon the speaker, for example, by means of screws I9 which secure it to the edge of the speaker frame adjacent the periphery of the cone.

The central portion of the cover I8 is provided withopenings 2t for the egress vci sound from the speaker. The cover 18 is preferably of inverted dish shape and it extends downwardly towards the base ii. The lowest portion of the cover I8 is of diameter somewhat larger than the base l i so as to provide an annular opening 2| for the egress of sound waves from the lower side of the speaker cone. The base l! serves to provide a mounting for radio apparatus such as radio tubes, transformers, a vibrator and the like, which will hereinafter be described in greater detail.v Such radio apparatus is located in a ring around the pot i5 of the loud speaker, being located within the annular space between the loud speaker and the cover I 8. It will readily be understood that such radio apparatus may be rendered .available for adjustment, replacement and the like by merely removing the cover i8, which may be done by taking out the screws l 9.

Owing to the fact that it is preferred to tune the receiver in the remote control unit, it is not necessary to mount a variable condenser in the main unit as in the case of the aforesaid copending application, The remaining radio apparatus is more convenient to this manner of assembly and the dimensions of the main unit may be somewhat reduced.

Energy is supplied to the main unit lli by a cable 22. For a set employing the wiring diagram of Fig. l, this cable comprises a conductor 23 and a conductive shield 2li, insulated from each other by suitable insulation. The conductor 23 and shield 2li are connected to a battery 25 inv the manner shown in Fig. 1. The main unit lil is connected to the remote control unit 26 by means of a iiexible cable 2l of suitable length. The number and relation of conductors in this cable depends upon the wiring system employed and will be discussed further in relation to the wiring diagrams shown in Figs. l, 2 and 10.

The remote control unit 2S contains a thermionic tube 23 and a variable condenser 22, which usually comprises a plurality of units ganged together, The wiring diagram shown in Figs. 1

and 2 call for three-gang condensers. The condenser shaft 30 carries a pointer 3| which cooperates with a scale 32. The condenser shaft 39 is actuated from a control shaft 33 by means of friction wheels 34. At its outer end the condenser control shaft 33 carries a manual control knob (not shown). A manual volume control is provided in the remote control unit 28. This control may comprise a knob 35 and a rheostat or potentiometer 36 actuated thereby. The scale 32 may be provided with suitable indicia and is preferably translucent. An incandescent lamp 31 is provided to illuminate the scale 32 on the inside. The remote control also comprises a switch 38, the function of which will be more readily understood with reference to the wiring diagram shown in Figs. l and 2.

Referring more particularly to the wiring diagram shown in Fig. 1, the receiver herein illustrated is a superheterodyne set o-f which the tube 28 in the remote control unit 26 is the oscillator and first detector. The tubes 39, 48 and 4|, which are located in the main unit, are intermediate frequency amplifying tubes. 'I'he tube 42 is the automatic volume control diode. The tube 43 is a four-element tube serving the purpose of second detector. The last tube 44 is an audio frequency power tube, the output of which is supplied to the Voice coil of the loud speaker I6 through an output transformer 45.

The antenna conductor 46 preferably enters the cable 21 in or near the main unit and extends through the cable to the remote control unit 26, being connected therein to a primary coil 41 of the antenna input system which is of lower impedance than would be required to match the antenna employed, in View of the capacity through the cable. The coil 41 is inductively coupled to a coil 48, which is tuned by a condenser 49, one of the gang of condensers referred to generally by the reference numeral 29. The coil 41 is connected to a point of the coil 48 comparatively near the grounded end thereof through a condenser 52, for the purpose of maintaining the impedance through the coil 48 lower than the total impedance of the coil. The coil 48 is inductively coupled to a coil 58 which is tuned by a variable condenser also one of the gang of condensers 29.

'The coil 58 is connected to the grid of the tube 28 and the plate of the tube 28 is connected in series with coils 53 and 54 and conductor 55 which extends through the cable 21. The coil 53 is coupled with the coil 56, which will be more fully described hereinafter. The coil 54 is coupled with coils 51 and 58. Coil 58 is tuned by condenser 59, which is the third of the gang of condensers designated 29. The output of the tube 28 energizes coils 54 and 58, which in turn energizes feed-back coil 51, causing tube 28 to oscillate. The result of this oscillation, in combination with a signal, is the production of current of intermediate frequency in coil 53, which in turn is communicated to coil 56 fo-r transmission to the main unit.

The switch 38 is connected to conductors 68 and 6| which extend through the cable 21. The volume control 36 comprises a resistance 62, one end of which is grounded, and a conductive arm 63 which cooperates with said resistance. The arm 63 is connected to a conductor 64 which extends through the cable 21. The conductor 64 is connected through a low resistance 88 to the cathode of tube 4|. This cathode is also connected through a high resistance 89 to the screen voltage line 98. The cable 21 also includes a conductor 65 which supplies filament current from the main unit to the tube 28. Conductor 55, previously referred to, supplies B current from the main unit to the plate of the tube 28.

The remote control unit is preferably contained Within a metallic housing 66 which is conductive- 1y connected to a ground conductor 81, which is preferably a metallic shield, extending between the remote control unit 26 and the main unit lll through the cable 21. This shield contains the conductor 68 which carries the output from the coil 56 to a coil 69 in the main unit. The conductor 68 is connected to one end of the coil 56, the other end of this coil being grounded, preferably through the shield 61. The shield 61 effectively prevents any undesired signals from being picked up by the conductor 68 and introduced into the input of the intermediate frequency amplifying tubes 39, 48 and 4|.

The main unit i8 will now be described. The coil 89 is inductively coupled to the coil 18 which is connected to the input cf the tube 39. The plate circuit of the tube 39 is coupled with the input of the tube 48, and so forth for the remaining tubes 4|, 43 and 44.

The tube 42 is the automatic volume control diode, the plate circuit of which is connected by a resistance 1| to ground. This plate circuit receives energy from the plate of the tube 48 through a condenser 12. The plate of the tube 42 is conductively connected through a resistance 13 to the input of the tube 48 and through a suitable resistance to the input of the tube 39. An intermediate point of the resistance 1| is conductively connected to the input of the tube 4|.

The main unit ||l comprises an interrupter 14, a transformer 15, and a rectifier 16 which is associated with coils 11 and condensers 18 for the purpose of ironing out fluctuations in the direct current and potential delivered by conductor 19. This conductor is connected in known manner to the plate circuits of tubes 28, 38, 48, 4|, 43 and 44. The filament current for all the tubes is derived from the battery 25 through conductor 88 which passes to the main unit I8, and is connected therein to the conductor 68. When the switch 38 is thrown to made position, the conductor 88 is connected to conductor 6| of the cable 21 and to conductors 8| and 82 in the main unit li). The current for the lament of tube 28 ows back to the control unit through conductor 85 of the cable 21. The conductor 82 is connected to the primary of the transformer 15, the other end of the primary being connected to the vibrator or interrupter 14, which in turn is connected to the other lead 83 of the battery, which is grounded.

The vibrator or interrupter 14 comprises a casing 84 including sound insulating material, in which is enclosed .an electro-magnet which controls points 86 in series with the winding of said magnet so as to cause continual interruption in the current flowing through the primary of the transformer 15. A condenser 81 and high resistance 88 are provided both across the winding 85 and points 86. The conductor 8| is also connected to the field winding of the speaker I6, the other end of this winding being grounded.

It is to be noted that one side of the tube filaments is grounded and the other side of the filaments is connected to the line 8|, the filament l of tube 28 being connected thereto by line 65 of cable 21. and the filament of tube 16 being connected thereto by line 82. Choke coils 9| are the output of the tube 40 into the tube 4|.A In

provided in the lament current circuit, being preferably arranged in series in the lament supply circuit, serving with the filament resistances to provide an induction-resistance filter which effectively lters out high frequency disturbances produced by the vibrator 14 and other causes. It will be seen that the filtering effect isgreatest towards the input end of the receiving set, where any disturbance present would be amplied tol the greatest extent.

The choke coil 92 is connected in series with the lead which supplies plate current to the tube 28. This choke coil prevents oscillation which might be caused by disturbances passing through lead 55, coil 53 and the plate ground capacity of the tube 28.

It is preferred that the rectifying tube 16 passes current when the points 86 make contact, rather than when they break Contact. The change from one condition to the other may be effected in many ways, one way being to reverse the connections of the secondary Winding of the transformer 75. The set can thus be readily adapted for any automobile, regardless ofwhich pole of the battery is grounded.

The operation is as follows: The switch 38 being closed, the circuits through the filaments are made, likewise the circuit through the vibrator or interrupter '|4, so that an interrupted current passes through the primary of the transformer '15. The voltage of this current is stepped up in the secondary of the transformer and is rectified in tube 'i6 so as to provide B voltage by means of conductor l0. The eld winding of the speaker i6 is energized and the desired station can be tuned in by actuating the gang of condensers 29. The volume level control 63 adjusts the relative grid bias of tube 4| by making the cathode more or less positive. It is to be noted that this control in the main unit is effected from the control unit by variation of a direct current which is of practically constant value for any particular manual setting of the volume level control 63. l

Th embodiment of the invention diagrammatically shown in Fig. 2 is largely similar to that shown in Fig. 1 and similar reference numerals .are employed to designate similar parts. In this embodiment the antenna lead 46 is conveyed through the cable 2l within a grounded metal shield 93, for the purpose of preventing the antenna lead 46 from picking up electrical disturbances.

In this embodiment the tube 42 is dispensed with and the tube 43 fulfills the functions of the tubes 42 and 43 in the embodiment of Fig. 1. This tube 43 contains two diodes and a triode in the'same envelope, all having a common cathode. One diode plate 94 serves as a second detector, the other diode plate 95 serves as a source of automatic volume control potential which is applied to the grids of tubes 39 and 40, a portion thereof being applied to the grid of tube 4| as in the previously described embodiment.

The triode elements of tube 43 act to amplify the output of the diode constituted by plate 94 and the cathode at audio frequency. The detected signal appears across the resistance 96 and is impressed upon the grid of the tube 43 through the lter resistor 91 and the capacity 98. The output transformer 99 of the tube 40 `steps down the output of that tube and feeds a the rst place, excessive difference of potential between the diode plates 94 and 95, which might cause oscillation in the tube 4|, is avoided. In the second place, the grid swing of the tube 4| is kept relatively small. The tube 4| is of the variable mu type so that volume level control may be effected by varying the amplification through control of the cathode potential relative to the grid.

Owing to the non-linear characteristic of this tube it is desirable to limit the grid swing to avoid distortion. This is accomplished by impressing a stepped-down signal on the grid of tube- 4| and then amplifying the signal up again to the desired value in the tube 4| and the transformer IBI, from which it is impressed upon the diode plate 94, which acts as the second detector. The transformer S9 includes a secondary winding E02 which supplies potential to the diode plate 95 which is rectified and appears across the resistance |63. This direct current potential is utilized for automatic volume control, as previously described.

In this embodiment of the invention the eld of the loud speaker comprises two windings |04 and |05. The winding |04 is connected in series with the plate voltage supply from the secondary of the power transformer 15 through the rectiiier tube T6. The winding |04 acts as a chokle coil to lter the plate supply, as well as supplying part of the energy to the speaker eld. Only a part of the speaker field energy is supplied from the plate supply, the remainder for bringing the speaker to the proper sensitivity being supplied directly from the battery to the coil |05. By properly proportioning these coils, the speaker field can be employed as a choke coil and the proper speaker sensitivity attained with a vibrator of moderate output.

To avoid operating the vibrator without a load, it is desirable that the iilaments of the tubes should have attained their operating temperature before the vibrator is connected to the battery. A thermostatic relay |56 fullls this purpose. This relay is adapted to be operated by a heating winding |01 which is energized upon the closing of the switch 38. The winding |07 is in parallel with the laments of the tubes and the current therefor is derived from the battery. The thermostatic relay is proportioned to close the vibrator circuit after the cathodes have attained operating temperature. The thermostatic switch is preferably temperature compensated so that its time interval is not excessively affected by changes in atmospheric temperature.

The thermostatic relay serves both as a delayed switch and as a remotely controlled relay. The vibrator current does not pass through cable 21, thus reducing the liability of the introduction or undesirable electrical disturbances into the amplifier tubes.

The battery cable |08 comprises three leads i60, H0 and lli, surrounded by a shield H2, one end of which connects to the chassis of the 'main unit, and the other to the grounded terminal of the battery. The conductor it is connected to the ungrounded terminal of the battery and leads to the switch 38 for the filament and heating element il supply. Conductor H0. is connected to the positive terminal of the battery and leads to one contact of the thermostatic relay |05, through which it is connected in parallel through the primary winding of the transformer 'i5 and vibrator 'I4 on the one hand, and through coil H15 on the other hand, to conductor Hl which is connected to the negative terminal of the battery. In Fig. 2 I have shown the negative terminal of the battery to be grounded.

Should the automobile be one in which the positive terminal is grounded, then shield H2 and conductor H should be connected to the positive terminal of the battery, and conductors l09 and Hl should be connected to the negative terminal of the battery. It is to be noted that this hook-up follows the nomenclature or" the preceding paragraph, according to which shield H2 is grounded and conductor E69 is connected to the ungrounded terminal, and lead E i0 is connected to the positive terminal while lead HI is connected to the negative terminal.

The operation of this embodiment will readily be understood from` the foregoing description and its similarity to the embodiment of the invention first described. It will readily be understood that when the switch 33 is closed, the laments begin to light up and the element |91 begins to heat. By the time the filaments have attained their operating temperature the thermostatic switch H66 has closed, completing the circuit through the vibrator T4 and the primary of the plate supply transformer l5, as well as through eld coil 65. Tuning is effected by means of the gang of condensers 49, 5I and 59, and manual volume control is effected by means of rheostat 63, in the manner described above.

For the satisfactoy transfer of signal energy from the control unit to the main unit, it is desired to employ means for minimizing loss or attenuation through the cable. In Figs. 6, 7, 8 and 9 are shown four circuits which may advantageously be used to attain this result under various conditions. The circuit shown in Fig. 6 is employed in the embodiments of the invention shown in Figs. l and 2. The common advantageous feature of all these circuits is that the voltage difference between the conductors within the cable, is substantially lower than the voltage across the circuits in the control and main units, to which the conductors connect or to which they are coupled. This low voltage difference reduces the attenuation or loss through the capacity of the conductors in the cable. However, as a high voltage is desired for the input to the amplifier in the main unit, the voltage should again be raised at the main unit end of the cable. The ratio of the voltage in the control unit and the main unit to that in the cable should be great enough to avoid undue losses through the capacity of the cable, but not so great as to cause undue resistance losses, resulting from very high currents flowing through these conductors.

The choice of the circuit to be used in a given set is dependent upon several factors, such as cost, permissible variation of characteristics, the degree of selectivity desired, the tubes employed, the characteristics of the cable, etc.

Where the capacity of the conductors of the cable is small, the structure of Fig. 8 may be employed. The structure of Fig. 9 is suitable with a cable of substantially fixed capacity. This permits of very simple coils in the output of the control unit and the input of the main unit. The structure of Fig. 6 permits of large capacity in the cable which does not have to be of a particularly exact value. The structure of Fig. 7 is highly advantageous when a high degree of selectivity is desired.

Fig. 8 embodies direct coupling; Fig. 9, capacity coupling; Fig. 6, inductive coupling, and Fig. 7 coupling by means of a tuned link circuit.

Minimum losses or attenuation are obtained when the reactance at the intermediate frequency connected to one end of the cable is equal to the reactance connected to the other end of the cable, the value of this reactance being determined by the electrical characteristics of the cable. For minimum losses the values of the various elements are so selected that if the cable is cut at any point, the reactance at the intermediate frequency looking into the cable on one side of the cut is equal to the reactance looking into the cable on the other side of the cut, but if the reactance in the first case is capacitive, the reactance in the second case must be inductive, and vice versa.

In the diagram shown in Fig. 6, the windings 53 and 56 have their coelicient of coupling as high as possible, likewise the windings 69 and l0. The step down of voltage between windings 53 and 56 and the step up between windings 69 and 'lil is preferably of substantially similar magnitude. In actual practice I have obtained excellent results with a circuit with a step down of 25 times and a step up of 25 times, using a tube of type R. C. A. 236 at 28 and a tube of type R. C. A. 239 at 39. As a result of the high step down the capacity between the conductors 6l and 68, illustrated as a phantom capacity at H3, is not critical and may vary Within considerable limits without greatly affecting the tuning of the circuits including the winding 53 and winding 19.

In the diagram shown in Fig. '1, the step down from winding 53 to winding 56, and the step: up from winding 69 to winding 10 is lower than in the case of Fig. 6, the number of turns in windings 56 and 69 being suitably increased to attain that result. In this case the inductances of windings 56 and 69 are so considerable that they and the conductors 61 and 68 connecting them constitute a link circuit which must be tuned to the intermediate frequency to give best results. Such tuning is highly advantageous in that it enables a very high degree of selectivity to be attained, since it provides the added selectivity of an additional tuned circuit without additional parts. The tuning of this circuit requires a capacity between the conductors 6l and 68, which capacity is shown in phantom at H4, to have a definite value.

Thus in the case shown in Fig. 6, the length of the cable is immaterial within considerable limits, but in the case of Fig. 7 the length of the cable is important for best results and if any considerable deviation from the optimum is attempted, correction of the capacity should be made in some manner as, for example, providing a condenser between the leads 6l and 68 at either end, or by selecting a cable of more suitable capacity characteristics.

The structure diagrammatically shown in Fig. 8, in which direct coupling is employed, is particularly suitable for use with tubes 28 and 39 of low impedance. In this arrangement coils 53 and 10 are connected by the leads 6l and 68, condensers H5 and H5 being provided in the lead 6B, that is, the ungrounded lead. The condensers i I5 and l i6 are 0f large capacity relative to the capacity of the cable, as indicated in phantom at l l'l. As the capacity of the cable is small, relative to the capacities H5 and H6, the system is independent to a considerable degree of the capacity between the leads 6l and 68.

The structure diagrammatically shown in Fig. 9, in which capacitative coupling is employed, is adapted for use when the tubes 28 and 39 are of high impedance. The windings 53 and 19 are of high inductance and the condensers I I8 and H9 are of relatively low capacity relative to that between the leads 61 and 68, which is indicated at |28. Under these circumstances two separate circuits are formed with the capacity |20 common to both and forming the coupling link therebetween. Here the capacity of the cable must have a relatively definite value in comparison with the capacity I l1 of Fig. 8.

The voltage between the conductors 61 and 68 is maintainedlow in the circuits shown in Figs. 6, '1, 8 and 9, and attenuation of the signal currents in passing through the cable is thereby substantially minimized. In the structures o-f Figs. 6 and 7 this low voltage relation is secured by stepping down the voltage across the Winding 53 to a lower voltage across the coil 56. In the structure of Fig. 8 the potential drop across the winding 53 is substantially equal to the potential drop across co-ndenser H5, and the potential drop across the winding 19 is substantially equal to the potential `drop across cone denser H6. In the structure of Fig. 9 a similar relation exists between the winding 53 and condenser H8 on the one hand, and between winding 10 and condenser I I9 on the other hand. In both cases the potential of the leads 61 and 68 is substantially equal.

It is not intended to limit the invention to automobile radio receivers, since it may be applied to home sets and indeed to any manner of set employing a remote control.

In the embodiment of the invention illustrated in Fig. 10, the main unit is substantially similar to that shown in Fig. 2. The principal difference is that the automatic volume control is applied to the tube 28 in the remote unit as well as tubes in the main unit. By this expedient the tube 49 may be omitted from the main unit while maintaining an ample amount of automatic volume control. For the sake of simplicity I have shown the power supply system of Fig. 1 in this embodiment.

The automatic volume control voltage is rectified at the plate 95 of the tube 43 and is applied to the grids of the tubes 39 and 4| in the manner described above with respect to the embodiment shown in Fig. 2. That is, the whole automatic volume control voltage is applied to the grid of tube 39 and a part thereof, determined by the resistances |2I, |22 and |23, is applied to the grids of tube 4| and the tube 28 in the control unit by means of the lead |24, an additional conductor which passes through the cable 21.

The tube 28 in the remote control unit is a six-element tube comprising a cathode |25, plate |26, control grid |21 and screen |28, an oscillator grid |29 and an oscillator plate |30. The oscillator grid |29 and oscillator plate |39, to* gether with the cathode |25, serve as oscillator elements independent of the control grid |21, so that the bias of the grid |21 can be varied to obtain automatic volume control without interfering with the local oscillation. The electron stream reaching the plate |26 is affected both by the local oscillation frequency and the signal frequency on the grid |21 in such a way that the intermediate frequency appears arcoss the coil 53 and 'is transferred to the coil 56. The intermediate frequency passes from the coil 56 through conductor 68 to the input of the tube 39.

Itis not intended to be limited to this particular type of tube since other tubes may be employed if desired, provided the bias of the control grid can be sufficiently varied without impairing the local oscillation.

Although the invention has been described in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention, except in so far as set forth in the following claims.

Having thus described my invention, What I claim and desire to secure by Letters Patent of the United States is:

1. A radio receiver comprising a control unit and a main unit, a cable connecting said units, a coil in the control unit, a coil in the main unit, conductors connecting said coils extending through said cable for transmitting signal energy from one unit to the other, a condenser in each unit in series with one of said conductors, means in the control unit for producing signal energy of definite intermediate frequency and supplying same to the first said coil, said coils, condensers and conductors constituting a circuit tuned to that frequency.

2. A radio receiver comprising a main unit and a control unit, a cable connecting said units, an antenna connected to said cable at or near the main unit, an antenna conductor extending therefrom to the control unit through said cable, a transformer in the control unit to the primary of which said conductor is connected, said primary having an impedance lower than would be required to match the antenna, a variable tuning condenser connected across the secondary of the transformer, and a condenser through which the ungrounded end of said primary is connected to an intermediate point of the secondary.

3. A radio receiver comprising two separate and independent units, one being a main unit and the other being a control unit, and a cable connecting said units; a thermionic tube in each unit, variable tuning meansv in said control unit for selectively receiving signal energy at a plurality of frequencies, a step-down transformer in the control unit having a primary coil and secondary coil and means to tune the primary coil, said step-down transformer receiving energy of a constant intermediate frequency from the tube in that unit, a step-up transformer in the main unit having a primary coil and a secondary coil and means to tune the secondary coil, means coupling the tunable primary and secondary coils to the respective thermionic tubes; and two conductors in said cable connecting the other coils of said transformers, the constants of said last-named coils, conductors, and associated elements being such that if the conductors are cut at any point in the cable, the reactance at said intermediate frequency looking into the ends on one side of the cut will be substantially equal and of opposite sign to the reactance looking into the ends on the other side of the cut.

4. A radioreceiver comprising a main unit and a remote control unit, thermionic tubes in the main unit, a multigrid thermionic tube in the remote unit serving as an oscillator and first detector, a cable having a plurality of conductors electrically connected to said units, means in the main unit for generating an automatic volume control voltage, one of said conductors being connected to one of the grids of the multigrid tube in the remote control unit to supply automatic volume control voltage thereto to vary its amplification.

5. A radio receiver comprising a main unit and a remote control unit, thermionic tubes in the main unit, a multigrid thermionic tube in the remote unit serving as an oscillator and rst detector, a cable having a plurality of conductors electrically connected to said units, means in the main unit for generating an automatic volume control voltage, one of said conductors being connected to one of the grids of the multigrid tube in the control unit to supply automatic volume control Voltage thereto to vary its amplification, and a volume lever control in the control unit, another of said conductors connecting the volume level control to a tube in the main unit to varythe gain of the amplifying system in the main unit.

6. A superheterodyne radio receiver comprising a control unit and a main unit physically separated but connected together by a multiconductor cable, tuning means for selecting a single signal, means including a thermionic tube for converting said single signal to intermediate frequency energy, and a transmission system comprising a coil tuned to said intermediate frequency in one unit, a coil tuned to said intermediate frequency in the other unit and conductors extending through the cable and connecting said coils, said transmission system having electrical characteristics such that if the conductors are cut at any point in the cable the reactance at said intermediate frequency looking into the ends on one side of the cut will be substantially equal to and of opposite sign to the reactance looking into the ends on the other side of the cut.

7. A superheterodyne radio receiver comprising a control unit and a main unit physically separated but connected together by a multiconductor cable, tuning means for selecting a 'single signal, Ameans including a thermionic tube for converting said single signal to intermediate frequency energy, a coil tuned to said intermediate frequency in the control unit and a coil tuned to said intermediate frequency in the main unit, conductors running through said cable connecting said coils, means for keeping the voltage between the conductors lower than the voltage across either coil, the conductors and associated elements having electrical characteristics such that if the conductors are cut at any point in the cable the reactance at said intermediate frequency looking into the ends on one side of the cut will be substantially equal to and of opposite sign to the reactance looking into the ends on the other side of the cut.

8. A radio receiver comprising two separate and independent units, one being a main unit and the other being a control unit, and a relatively long cable connecting them, thermionic tube means in the control unit adapted to receive signal energy at a plurality of frequencies and convert the energy into a single intermediate frequency, voltage step-down means in the control unit including coupled primary and secondary coils with means to tune the primary coil, ther- A mionic amplifying means in the main unit, voltage step-up means including coupled primary and secondary coils with means to tune the secondary coil in the main unit connected thereto, and a transfer circuit comprising the rst said secondary coil, the last said primary coil and a pair of conductors extending through said cable, the constants of the transfer circuit and the circuits coupled thereto having such correlated values that if the conductors are cut at any point in the cable, the reactance at Said intermediate frequency looking into the ends on one side of the cut will be substantially equal to and of opposite sign to the reactance looking into the ends on the other side of the cut.

9. A radio receiver, comprising a control unit and a main unit, a cable connecting said units, a coil in the control unit, a coil in the main unit, conductors connecting said coils extending through said cable for transmitting signal energy from one unit to the other, a condenser in each unit in series with one of said conductors, means in the control unit for producing signal energy of definite intermediate frequency, and supplying same to the rst said coil, and mea-ns for adjusting the capacity between the conductors of the cable to tune the circuit comprising said coils, condensers and conductors to said definite intermediate frequency.

10. A radio receiver comprising a control unit and a main unit, a multi-conductor cable connecting said units, selective means in said control unit tuneable to a plurality of stations transmitting signals at different frequencies, means in the control unit for converting said different frequencies to signal energy of a definite intermediate frequency, a coil and a condenser in the control unit, a coil and a condenser in the main unit, conductors coupling said coils extending through said cable for transmitting signal energy from one unit to the other, said coils, codensers and conductors comprising a coupling circuit tuned to said intermediate frequency and transmitting said intermediate frequency from said control unit to said main unit.

11. A radio receiver comprising a control unit and a main unit, a multi-conductor cable connecting said units, selective means in said control unit tuneable to a plurality of stations transmitting signals at different frequencies, means in the control unit for converting said different frequencies to signal energy of a definite intermediate frequency, a transformer in said control unit having a condenser connected across its primary, a transformer in said main unit having a condenser connected across its secondary, conductors connecting said transformers extending through said cable for transmitting signal energy from one unit to the other, said transformers, condensers and conductors comprising a coupling circuit tuned to said intermediate frequency and transmitting said intermediate frequency from said control unit to said main unit.

EDWARD F. ANDREWS. 

